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The amount of kyanite in samples obtained from magnetic and density separations of a kyanite ore was established by a quantitative X-ray diffraction procedure employing an internal standard. The accuracy of the results at low kyanite levels was improved by adding pure kyanite to the samples, analyzing these mixtures and extrapolating back to the lower level. The results were verified by X-ray diffraction analyses of synthetic mixtures containing amounts of kyanite approximately equal to that indicated in the ore samples. The percentage of error is estimated to be ±3per cent of the amount present in the range of 20 to 80 per cent kyanite.
We present results from a multiwavelength study of the blazar PKS 1954–388 at radio, UV, X-ray, and gamma-ray energies. A RadioAstron observation at 1.66 GHz in June 2012 resulted in the detection of interferometric fringes on baselines of 6.2 Earth-diameters. This suggests a source frame brightness temperature of greater than 2 × 1012 K, well in excess of both equipartition and inverse Compton limits and implying the existence of Doppler boosting in the core. An 8.4-GHz TANAMI VLBI image, made less than a month after the RadioAstron observations, is consistent with a previously reported superluminal motion for a jet component. Flux density monitoring with the Australia Telescope Compact Array confirms previous evidence for long-term variability that increases with observing frequency. A search for more rapid variability revealed no evidence for significant day-scale flux density variation. The ATCA light-curve reveals a strong radio flare beginning in late 2013, which peaks higher, and earlier, at higher frequencies. Comparison with the Fermi gamma-ray light-curve indicates this followed ~ 9 months after the start of a prolonged gamma-ray high-state—a radio lag comparable to that seen in other blazars. The multiwavelength data are combined to derive a Spectral Energy Distribution, which is fitted by a one-zone synchrotron-self-Compton (SSC) model with the addition of external Compton (EC) emission.
The Tasmanian Cenozoic macrofossil record is relatively rich, and changes that have occurred in the vegetation of the region are becoming increasingly well understood. The record is essentially one of rainforest elements, especially in the Paleogene, but taxa that are now common in sclerophyllous heathlands and woodlands are increasingly prevalent in Quaternary sediments.
Extant Tasmanian rainforest is renowned for its beauty, and botanists have long recognised its marked taxonomic and structural similarity to other southern hemisphere ‘cool temperate’ forests of New Zealand and Chile. These are generally dominated by Nothofagus trees, their boughs laden with lichens and verdant shrouds of bryophytes. Other links are often made by phytogeographers to similar forests in high altitude regions of northern New South Wales and the much more species-rich vegetation of the generally montane regions of New Guinea and New Caledonia where Nothofagus also grows. A striking aspect of these forests is the presence of a variety of conifers, principally Podocarpaceae, but also Cupressaceae and Araucariaceae. In Tasmania the Araucariaceae are extinct, but the region is unique in the southern hemisphere in having a genus of Taxodiaceae, Athrotaxis. Athrotaxis spp. are often associated with Australia's only winter deciduous plant, Nothofagus gunnii, in montane regions of the island. The macrofossil record shows conclusively that the current diversity of Tasmania's woody rainforest flora is very much lower than at any other time during the Cenozoic. It confirms that there are strong floristic links to regions as widespread as eastern and southwestern mainland Australia, southern South America, New Zealand and New Guinea. In fact, Tasmanian Paleogene floras contain a wealth of taxa that are closely related to plants now confined to these regions.
Apart from the relatively large tracts of rainforest in Tasmania, closed forest lacking eucalypts is now confined to small patches along the east coast of Australia. In contrast to mainland Australia, Tasmania is relatively mountainous and has a well-developed woody alpine vegetation, dominated by shrubs of the Asteraceae, Epacridaceae, Myrtaceae and Proteaceae.
A preliminary orbit has been derived for the high luminosity, 27-d classical Cepheid T Mon. Velocities for the hot companion have been measured from an HST GHRS spectrum and 3 IUE spectra. The companion velocities are inconsistent with binary orbital motion and it is likely that the companion is itself a short period binary. The HST spectrum also shows that the companion is a chemically peculiar star, probably magnetic.
IAU Commission 29 - Stellar Spectra has been one of the IAU commissions from the onset, until its dissolution at the most recent IAU General Assembly in Honolulu in 2015. This commission belonged to IAU Division G (“Stars and Stellar Physics”), the latter committed with fostering research in stellar astrophysics. Within the general field of stellar astrophysics, stellar spectroscopy plays a key role, as stellar spectra are a powerful tool providing a view into the detailed physical properties of stars and the physical processes occuring within them.
For over a decade, the structure of the inner “hole” in the transition disk around TW Hydrae has been a subject of debate. To probe the innermost regions of the protoplanetary disk, observations at the highest possible spatial resolution are required. We present new interferometric data of TW Hya from near-infrared to millimeter wavelengths. We confront existing models of the disk structure with the complete data set and develop a new, detailed radiative-transfer model. This model is characterized by: 1) a spatial separation of the largest grains from the small disk grains; and 2) a smooth inner rim structure, rather than a sharp disk edge.
Findings from the first two years of a long-term study of conifer log decomposition are presented. Log decomposition is regulated by the physical and chemical states, and development of decomposer foodwebs. The functional group with the greatest initial effect on the log is the channelisers, represented in our study by ambrosia and bark beetles. They not only create multitudes of channels into the logs but vector the initial decomposer community. Ambrosia beetles exclude certain elements of the decomposer community from channels until they vacate the log, at the end of their reproductive phase. The foodweb during the early stages of decomposition includes nitrogen-fixing and other bacteria, fungi, protozoa, nematodes, and arthropods. Seasonal fluctuations of temperature and moisture are hypothesised to work in tandem to modulate the activities of the decomposer community.
Czochralski silicon was implanted with oxygen at 0.4 and 3.5MeV to obtain concentrations near 1020 oxygen/cm3 in the implanted region. Following implantation the wafers were aged at about 1000°C for 7 hours, and the resulting precipitates were examined by HREM. A high density of octahedral SiOx precipitates (∼1015/cm3) was the dominant morphology. Plate type precipitates and dislocations were also present at lower density. The data indicate octahedra grow from the plates.
Deposition of Au on exsitu cleaned (100) Si wafers resulted in the formation of a discontinuous polvcrvstalline Au layer containing lattice defects. On parts of the interface Au and Si were separated by a thin oxide layer, but elsewhere were in direct contact, with no evidence of metastable phase formation. Post deposition heating to 1000°C. well above the 370°C eutectic temperature of the system, caused formation of a reaction zone at the interface, and disappearance of the thin oxide layer. No amorphous phases formed during cooling. Quenching produced small Au precipitates in Si-rich regions. If the wafer contained dislocations. Au precipitation was observed on subboundaries directly connected to the Au/Si interface, but not on dislocations remote from the interface.
Vacancy formation was studied in the refractory bcc metals, tungsten, chromium, and niobium, using the positron annihilation spectroscopy Doppler broadening technique, between room temperature and the respective melting temperatures, under ultra-high vacuum conditions. Temperatures were measured by optical and infrared pyrometry, a W(Rh) thermocouple, and the power delivered to the sample, with calibrations against known melting temperatures. For W, a trapping-model analysis of the data from the temperature range 300–3633 K yielded a vacancy formation enthalpy of 3.76 ± 0.39 eV. For Cr, a similar fit to the data from 296–2049 K yielded a vacancy formation enthalpy of 2.0 ± 0.2 eV. The results are discussed in relation to previous vacancy formation and self-diffusion studies. Measurements on Nb as a function of temperature and oxygen content are also presented.
XPS and LEED were used to study the adsorption and ordering of oxygen on Cu(11O) at 83±1 K and between 300 and 320 K and to follow changes in the oxygen coverage and surface structure produced by 5-min anneals at temperatures up to 880 K. The relationship between oxygen coverage and surface structure, as well as their mutual dependence upon exposure, surface temperature at exposure, and subsequent annealing treatment, is discussed.
We summarize the results of an extensive investigation on ion implanted arsenic in silicon after pulsed laser annealing and laser plus furnace annealing. The experiments are aimed at determining the structural and chemical environment around an arsenic impurity atom and relating that information to the electrical behavior of arsenic in silicon. We have implanted silicon with arsenic, 6×1016 As/cm2 at 100 KeV, followed by laser annealing, to obtain epitaxial regrowth with peak As concentrations of about 8 at.%. Subsequent furnace annealing at 800°C for 30 minutes reduces the apparent electrical activity of the arsenic atoms, increasing the electrical resistivity by a factor of three. We have used EXAFS, together with RBS and ion channeling, to investigate the structural and chemical origins of this deactivation. EXAFS measurements are consistent with As occupying tetrahedral sites in both laser ann-ealed and laser plus furnace annealed samples. Average As-As coordination numbers, found from fitting the EXAFS data, were 0.2 and 4.5 for nearest neighbors and for next nearest neighbors respectively. These coordination numbers suggest that there are regions with As concentrations much greater than the nominal maximum concentration mentioned above, and that the preferred local chemical order in regions of high As content resembles that in GaAs, with Si preferentially occupying Ga-sites. This short-range chemical order is unchanged by the furnace annealing. However, we find that furnace annealing does reduce the As-As second neighbor distance by approximately 0.1Å.
The structures of SiC/Si3N4 interfaces and Si3N4 matrix grain boundaries in Ceramic Matrix Composites (CMC) were investigated by high resolution electron microscopy. The light element chemistry of the interfaces was analyzed by high spatial resolution (∼3 nm) position resolved EELS in a field emission TEM and by high spatial resolution EDS in a dedicated scanning transmission electron microscope (STEM). High-angle annular dark-field (HAADF) imaging (resolution < 1 nm) technique was used to determine the distribution of yttrium atoms at matrix grain boundaries and at SiC/Si3N4 interfaces. HAADF images suggest that yttrium might diffuse into Si3N4 crystals bounding the interfacial and grain boundary regions.
Rutherford backscattering and ion channeling-axial scans have been used to study lattice sites for several impurities implanted into A12O3. The case of Ga implanted in A12O3 is discussed and is shown to be substitutional on the Al sublattice. Additionally, the use of this technique in the study of precipitates in A12O3 is discussed with reference to Fe implanted A12O3 which was annealed in either oxygen or hydrogen.
Thin films of titanium, platinum, and hafnium were deposited on single crystal n-type, (0001) 6H-SiC at room temperature in UHV. Microstructure and chemistry of their interfaces were analyzed by high spatial resolution TEM imaging and spectroscopy. Ti5Si3 and TiC were the two phases found in the reaction zone of Ti/SiC specimens annealed at 700°C. A carbon-containing amorphous layer formed between Pt and SiC when the annealing temperature went up to 750°C. There was no apparent reaction zone in Hf/SiC specimens annealed at 700°C for 60 min‥ The change of electrical properties of metal/6H-SiC devices was attributed to these new product phases.
The introduction of GaAs grown at low MBE growth temperatures has spurred considerable activity in attempts to understand conduction mechanisms and optical properties. In LT GaAs, the formation of microscopic As precipitates dominates the conductivity, producing electronic transport mainly by variable range hopping conduction. The resulting high resistivity and short carrier lifetimes have enabled the use of LT GaAs in FET buffer layers as well as in ultra-fast optical switches. An extension to AlInAs has also been performed and it was seen that variable range hopping is also present in the Asbased ternary.
We report the optical and electronic properties of InP grown at low temperatures in a gas source MBE using dimeric phosphorus produced from cracked phosphine. The conductivity is higher than the equivalent GaAs LT material and does not have the same temperature dependence. The conditions under which growth occurs ie, substrate temperatures, V/ill ratios and annealing is explored. The structural properties, temperature dependence of the conductivity, deep level structure and the photoluminescence properties of the material are also investigated.
Neutral, low-valent complexes of transition metals or an organometallic compound of Ge are prepared containing ancillary ligands which bear silicate ester or (alkoxy)silicon functional groups. Inclusion of these molecules as dopant species in a conventional sol-gel synthesis of silica xerogels affords silica xerogels in which dopant molecules have presumably been covalently incorporated into the xerogel matrix with uniform and high dispersion. Subsequent thermal treatment of these molecularly doped xerogels under reducing or oxidizing/reducing conditions gives nanocomposites containing nanoclusters of metals or semiconductor substances. By this procedure, nanocomposites containing nanoclusters of Ag, Cu, Pt, Os, CCo3, Fe2P, Ni2P, or Ge have been prepared. Preliminary evidence for the formation of a nanocomposite containing Pt-Sn nanoclusters derived from a bimetallic molecular precursor is also presented. Characterization data for the nanocomposite materials include TEM, electron diffraction, EDS, XRD, and selected use of micro-Raman spectroscopy. These results support the hypothesis that covalent incorporation of molecular precursors containing low-valent metals into a silica xerogel can afford nanocluster phases with high dispersion, relatively small particle size, and unusual elemental composition.
X-ray diffraction (XRD) is generally used to measure crystallographic texture, but complete analysis is rarely performed. Orientation imaging microscopy (OIM) gives similar data by electron diffraction and has potential for widespread use since it may be added to any scanning electron microscope. Analysis software has been developed to reduce QIM results into a form which may be compared directly to XRD results. OIM texture parameters measured from Al films showed good quantitative agreement with XRD parameters, however the texture in Cu films is more complex and difficult to compare. Although subject to certain limitations, OIM has several advantages over XRD including more efficient data collection, better sensitivity to minor texture components, and more flexible data analysis.
A collaboration between The Materials Research Science and Engineering Center (MRSEC) and the Integrated Science (IS) program run by the Center for Communication and Educational Technology (CCET) at The University of Alabama has been developing a computer game based approach to teaching Periodic Table concepts and facts to middle school students. The game is broken into seven different sections. There are three information centers, which are each paired with a game, and there is a “Dream Room” which provides an incentive for students to master the subject matter of the game. The three information centers focus on learning the elements, their positions in the periodic table, and trends in physical and chemical properties. The games then test the students' knowledge of the concepts and facts in the information centers. The game is currently in a late beta version and can be accessed over the web at http://www.mint.ua.edu/periodictable.
Preliminary results from a large evaluation exercise shows that classes that use the computer games improved significantly more on tests of subject matter than a control group.